Safety stop mechanism for hoisting machines



Patented Aug. 11, 1942 v SAFETY STOP `MECHANISM FOR HOISTI'NG MACHINESElwyn F. Bonney, Newton Lower Falls, Mass., as-

signor y,to Lewis-Shepard Company, Watertown, Mass., a corporation ofMassachusetts Application vJuly 16, 1940, Serial No. 345,777

3 claims. (o1. 1254-174) vThis invention relates to improvementsV insafety stop mechanism for hoisting machines, and the object thereof isto provide improved means for arresting the hoisting mechanism inresponse to'u'ndue slackening of the cable.

Usually electrically operated hoisting machines have a verticallymovable load supporting means and a cable and winch for raising andlowering the same, the winchis driven by an electric motor having in itskpower circuit a' reversing switch operable whenV swung in one directionfrom neutral position in which the switch is open to cause the motor torotate the Winch in a direction to raise the load supporting means andoperable when swung in the Vopposite direction to reverse the directionof rotation of the motor and winch to control the lowering movement ofthe load supporting means.

II" during its lowering the load supporting means engages an obstructionwhicharrests its downward movement the continued rotation Vof the winchwill slacken the cable unless and until the power circuit is broken. If,Where the cable is thus slackened, the load supporting means is releasedfrom the obstruction, the load supporting means and the load upon itwill drop and the momentum acquired may be suflicient to break the cableand injure the load supporting means or the load carried thereby.

I am aware that heretofore means have been provided which are voperableby the slackening of the cable under such circumstances to break thepower circuit to the electric motor. Such devices, however, are more orless complicated and require movements of such extent that considerableslackening of the cable will take place before the circuit to the motoris broken.

One of the objects of the present invention is therefore to provide asafety stop mechanism of suiiicicnt sensitiveness to operate promptlyupon the slackening of the cable to break the motor circuit.

Another object of the invention is to provide a simplified safety stopmechanism which may be associated with a commercial type of switchmechanism, preferably of the type in which an overload in the motorcircuit will cause the switch to break the motor circuit. y

These and other objects and features of the invention will more fullyappear from the follow- 'Y' ing description and the accompanying drawingand will be particularly pointed out in the claims.

A preferred embodiment of the invention is illustrated in theaccompanying drawing in which a sufficient portion o'f `a usual type ofhoisting machine is illustrated to show the application of the presentinvention thereto.

In lthe drawing:

Fig. 1 is a front elevation of a portion of the frame of a hoistingmachine having a winch and its cable, a switch box containing aconventional switch mechanism, and means engaging the cable operableupon slackening of the cable to cause the switch to break the motorcircuit;

Fig. 2 is a side elevation of thesame showing the relative positions ofthe winch and cable, an electrically operated mechanism for driving thewinch and the safety stop mechanism embodying the present invention;and,

Fig. v3 is an enlarged detail sectional View of a portion of the switchbox, the trip mechanism for a conventional stop switch in -the motorcir,- cuit and illustrating partially -in section the trigger mechanismand plunger for actuating the same to break the motor circuit.

As illustrated in the accompanying drawing the hoisting mechanismcomprises usual frame members -l and 2 having mounted therein Va shaft 3to -which is xedly secured a winch 4 which is driven from a shaft 5 ofan electric motor 6 through a chain 'La worm-8, and a worm gear 9. Thecable IIJ, which is secured to and woundupon the winch, extends upwardlyin the usual manner over a sheave mounted in the upper vportion of theframe (not shown) and thence downwardly to the load supporting means.The load supporting means is guided upon suitable uprights in the usualmanner.

The switch mechanism for controlling the motor circuit is contained in aswitch Vbox Il which is mounted upon aplate l 2 which is carried by across girderrof the frame and has bosses |250 projecting from theendsthereof on which a lever having a cable-engaging roller is fulcrumed, aswill hereinaftermore fully appear. v

-A suitable controller for reversing the direction yof the currentsupplied to the motor, which is enclosed in the switch box, may be ofany usual character having `a lshaft I3 .provided with a manuallyoperable .handle qI4 for moving the switch from .neutral position inywhich the motor circuit is'broken toa position in which the currentsupplied to the Ymotor will cause'the winding of the cable upon thewinch to raise vthe load supporting means and ywhen swung from neutralposition in the other direction to reverse vthe direction of current andthereby cause the winch to lower the load supporting means.

Theswitch box H of thepresent inventionalso contains aswitch in themotorcircuit which'may be operated manually to break the motor circuit andthe present invention comprises means operable by the slackening of thecable to cause the safety switch to break the motor circuit.

Any suitable sensitive type of safety switch having trigger mechanismfor breaking the motor circuit may be employed. In the illustrativeembodiment of the invention shown herein the safety switch is of thecommercial type manufactured by The Trumbull Electric ManufacturingCompany of Plainville, Connecticut, such as illustrated and described inPatent No. 1,886,477 granted November 8, 1932, to Benjamin E. Getchelland need not therefore be illustrated in detail. The switch illustratedin that patent is an overload switch adapted upon increase in thecurrent supplied to the electric motor in response to an overload uponthe motor to throw the switch to open position and thereby break themotor circuit. This switch is of the sensitive type in that the switchis maintained in open position by a latch |5, such as that shown in thepatent, which is held in operative position by a trigger |6 which ispivotally mounted at on brackets I8 extending downwardly into a recessI9 of a switch block 20 of insulating material. The trigger I6 has anextension 2| which is normally held by a spring 22 in a position inwhich the trigger IB supports the latch l and as disclosed in the patentto Getchell aforesaid thermostatic means are provided for tripping thetrigger, thus releasing the latch and causing the switch to break themotor circuit.

The thermostatic means for tripping the trigger I6 as illustrated hereinis substantially the same as that illustrated and described in theGetchell patent aforesaid and comprises a bimetallic thermoresponsiveelement 2|:c carried by a metal bracket which is mounted on the switchblock of insulating material and is connected at its lower free end toathreaded rod or bolt 22:1,` which extends axially through the spiralspring 22 and through the trigger extension 2|. The rod 22x is providedat its end with a suitable nut which clamps the trigger extensionagainst the end of the spring 22. A suitable heater element 220, in thecircuit which supplies the electric current to the motor, is located inproximity to and in parallelism with the thermostatic element 2|a: andoperates when heated by the increase in current when the motor issubject to overload to bend the bimetallic element in a direction whichwill move the trigger extension 2| in a direction (to the right Fig. 3)and thereby swing Fig. 3) out of engagement with the latch I5 thereuponcausing the switch mechanism to break the motor circuit in the mannerfully disclosed in the Getchell patent.

The present invention comprises a simple and effective means operableupon slackening of the cable to actuate the trigger mechanism of thesafety switch. It will be understood that while the Trumbull type oftrigger-actuated safety switch is referred to herein that the inventionthe trigger (to the left may be applied to otherwell known commercialtypes of sensitive trigger-operated switches.

The switch-actuating mechanism which is illustrated herein comprisesbroadly yieldably actuated means forcibly engaging the cable and meansoperable by the yielding movement thereof upon slackening of the cableto engage and trip the trigger, thereby to break the motor circuit. Inthe particular construction illustrated herein a plunger 23 of anysuitable material is 75 slidably mounted in a tubular guide 24 inalinement with the extension 2| of the trigger I6. The tubular guide 24as shown herein is mounted in a screw threaded sleeve 25 which extendsthrough the front wall 26 of the switch box and has an enlarged head 21engaging the outer face of the switch box and a clamping nut 28 mountedon the screw threaded portion of the sleeve rmly engaging the inner faceof the wall 26. Suitable means, such as cotter pins 29 and 30 areprovided to limit the movement of the plunger 23. The plunger 23desirably is provided with a rounded end portion 3| adapted to beengaged by suitable actuating means operating when the cable isslackened to force the plunger inwardly and thereby trip the trigger.

In the preferred embodiment of the invention which is illustrated hereinthe actuating means comprises a lever which, as illustrated herein, hasparallel arms 32 which are pivotally mounted upon a shaft 33 which isxedly secured in the ears |23: of the plate |2. The arms 32 of the leverare connected by aplate 34 and also at their ends by a tubular member 35which is welded to the arms 32 and in which is mounted a shaft 36 of acable-engaging roller 31 having a length at least equal to the width ofthe winch drum 4. The lever is so fulcrumed that when the roller engagesthe cable as illustrated in Fig. 1 it is held forcibly against thecable.

While the weight of the roller, if made of heavy material such as steel,may be suflicient properly to actuate the switch mechanism upon theslackening of the cable, additional means may be provided for moreforcibly holding the roller against the cable. In the constructionillustrated such means comprises a coiled spring 38 which is mountedupon the shaft 33 and secured at one end to one of the ears |21: of theplate I2, and at its other end engages the plate 34 which connects thelever arms 32. The lever is provided with an upward extension 39 whichprojects beyond the axis of the plunger 23.

The operation of the safety stop mechanism thus illustrated anddescribed will be obvious. The roller 35 is so suspended by the lever 32as forcibly to engage the cable at all times and its force of engagementmay or may not be augmented by that of the spring 38. If the loadsupporting means encounters an obstruction during its downward movementthe continued rotation of the drum will produce a slackening of thecable which will enable the roller 35 to swing outwardly, therebycausing the extension 39 of the lever 32 to force the plunger 23inwardly and trip the trigger mechanism, thus releasing the latch |5 andbreaking the motor circuit.

It will be understood that the particular embodiments of the inventionshown and described herein are of an illustrative character and notrestrictive, and that various changes in form, construction andarrangement of parts may be made within the spirit and scope of thefollowing claims.

Having thus described the invention, what is claimed as new, and desiredto be secured by Letters Patent, is:

1. Safety stop mechanism, for hoisting machines having a frame, a motoroperated winch mounted on said frame having a hoisting cable extendingupwardly therefrom, a switch box, mounted on said frame above said winchand in proximity to said cable, having therein a thermostatic overloadswitch in the motor circuit, means including a trigger for holding theswitch closed when the switch is moved to circuit-completing positionbut operable by the thermostatic means to trip said trigger and therebyopen the swtich in response to increase in the current due tooverloading of the motor, a plunger slidably mounted in said switch boxin alinement with said trigger, a lever fulcrumed on said frame havingan upwardly extending arm provided with means to engage and actuate saidplunger, and another downwardly extending arm provided with a rollerlocated between the fulcrum of the lever and the Winch to engage thecable and when the cable is taut to hold said lever at a substantialangle to the vertical with the plunger-actuating arm out of operativeengagement with the plunger and operable upon slackening of the cable tocause the plunger-actuating arm to engage and'actuate the plunger totrip the trigger and thereby cause the switch to open the motor circuit.

2. Safety stop mechanism for hoisting machines having a frame, a winchmounted on said frame having a cable extending upwardly therefrom, meansincluding an electric motor for actuating said winch, a switch boxmounted on said frameabove said winch and in proximity to said cable andhaving therein a switch for said motor provided with a trigger forholding said switch closed when the switch is moved to circuit-closingposition, thermostatically operable means for releasing said trigger inresponse to overload on said motor circuit thereby to cause the switchto break the motor circuit, and supplementary means operable in responseto slackening of said cable to release said trigger and thereby to causethe switch to break the motor circuit.

3. Safety stop mechanism for hoisting machines having a frame, a winchmounted on said frame having a cable extending upwardly therefrom, meansincluding an electric motor for actuating said winch, a switch boxmounted on said frame above said winch and in proximity to said cableand having therein a switch for said motor provided with a trigger forholding said switch closed when the switch is moved to circuit-closingposition, thermostatically operable means for releasing said trigger inresponse to overload on said motor circuit thereby to cause the switchto break the motor circuit, and supplementary trigger-tripping meanscomprising a plunger slidably mounted in the side of said switch boxadjacent to said cable and in alignment with said trigger, andplunger-actuating means having a roller to engage said cable andincluding means to lengage and actuate said plunger, and yieldable meansnormally holding said rollerforceably in engagement with said cable whentaut and retaining said plunger-engaging means in inoperative positionbut operable upon the slackening of the cable to cause theplunger-engaging means to actuate the plunger, thereby to trip theswitch and cause the switch to break the motor circuit.

ELWYN F. BONNEY.

